The present invention relates to a method and apparatus for controlling a gas turbine engine and more particularly, to a gas turbine system having an extraction channel for supplying part of the discharge air of a compressor to another installation and a method of controlling the same.
A gas turbine engine of the extracting operation type, in which part of the discharge air of a compressor is extracted and is used as a utility for another installation, is capable of supplying both power and high pressure air and performs an important role as the power/compressed air feed source of a plant. However, in a case where the amount of extraction air for another installation is relatively large and where the amount of extraction fluctuates conspicuously, a problem arises when the amount of combustor air to be supplied to the combustor of the gas turbine engine fluctuates widely, so that the normal continuous operation of the gas turbine engine is difficult.
As a countermeasure, it has been proposed to set upper and lower limit values for the flow rates of extraction and stopping operation of the gas turbine system when the amount of extraction falls outside the set limits. Alternatively, a bypass for connecting the discharge portion of the compressor to the exhaust the operation of the gas turbine is stopped. Alternatively, a bypass for connecting the discharge portion of the compressor to the exhaust portion of the gas turbine engine is provided, and an air release valve is interposed in the bypass, whereupon, when the flow rate of extraction falls short of the lower limit value, the air release valve is opened to release the air. A prior-art example concerning air release regulation is described in, for example, Japanese Patent Application Laid-open No. 259729/1985.
In the gas turbine engine of the extracting operation type, for the purpose of keeping a high efficiency the gas turbine engine, it is often the case that the designed flow rate of extraction is set at the beginning and that the specifications of the compressor and the turbine are determined on the premise of the flow rate of extraction.
In such a gas turbine engine, the continuation of the normal operation of the gas turbine engine becomes difficult in a case where the actual flow rate of extraction develops a great deviation relative to the designed value transiently or steadily.
It is presumed that the gas turbine is being operated at the designed flow rate of extraction under a certain load.
If, for any reason, the flow rate of extraction lowers drastically, the flow rate of the combustor air will increase and the discharge pressure of the compressor will rise without the air release valve. and, where the discharge pressure exceeds the upper limit of the allowable value thereof, surging might arise thereby leading to a serious accidental breakdown of the system.
On the other hand, if the flow rate of extraction increases drastically, the flow rate of the combustor air will decrease and, where the flow rate falls short of the lower limit of the allowable value thereof, the combustor and turbine portions might be damaged due to an excessive combustion temperature. Even the provision of the air release control channel which includes an air release regulating valve interposed in the path branched from a discharge portion of the compressor, cannot form a basic solution since, when the flow rate of extraction is too large, the role of protection cannot be performed, and, when the air is released with too small a flow rate of extraction, the gas turbine efficiency lowers drastically.